The present invention relates to one-part latex compositions prepared by a "core-shell" multistage polymerization process. In particular this invention relates to latices of polymeric particles having a polymeric core formed by polymerization of one or more ethylenically unsaturated monomers in the presence of an epoxy resin; and a polymeric shell formed on the core by emulsion polymerization of one or more thylenically unsaturated monomers and a hydroxyl or carboxyl functional monomer in the presence of the core, providing that the monomers in both the core and the shell do not contain amino functional groups; and post-adding an organic compound having amino functional groups, wherein the amino groups react with the epoxy resin upon drying to produce a crosslinked polymer product.
The one-part latex compositions of the present invention can be used as heat resistant, flexible binders in the formation of nonwoven mate; as laminating adhesives which form flexible laminates having high bonding strength and a high degree of humidity and water resistance; as laminates of woven and non-woven fabrics, coated and uncoated paper and paper boards, flexible films of polyethylene and the like.
The term core-shell structure has become well-understood in the art as defining a layered particulate composition having a polymeric center or core surrounded by a shell or overcoat formed of a second polymeric material. Methods for the preparation of such core-shell particulate compositions are well known in the art and include a variety of layered particulate materials having a core and one or more shell layers. For example, U.S. Pat. No. 3,661,994 discloses graft polymers formed by a sequential polymerization process, wherein a rigid, polymeric seed or core is surrounded by a graft polymerized rubber layer, and optionally encapsulated with a graft polymerized rigid outer layer. Fusion of the shell component occurs during thermal processing, such that the core-shell nature of the product is no longer discernable.
Japanese Patent No. 63-223018A also discloses the preparation of core-shell polymers. The core contains water insoluble epoxy resins dissolved in unsaturated ethylene monomer(s) which are polymerized to form emulsion polymer particles. The shell contains unsaturated ethylene monomer(s) having amine groups which are compolymerized with other unsaturated ethylene monomers. The weight ratio of the unsaturated ethylene monomer(s) to the epoxy resin in the core is 1:1 to 2:1, and the weight ratio of the unsaturated ethylene monomer(s) containing amine group(s) to the other unsaturated ethylene monomers in the shell is 1:99 to 25:75.
In an attempt to provide stable aqueous epoxy-containing emulsion systems which will thermoset on baking, the art has previously attempted to combine emulsions of acrylic copolymers, including an epoxy-reactive monomer (a maleic or fumaric half ester), with a separate emulsion of an epoxy resin as shown in Cline U.S. Pat. No. Re 25,880. However, when separate emulsions are used, many difficulties are encountered. First, these two emulsions frequently demand a large amount of emulsifying agent which degrades film properties. Also, compatibility with the high molecular weight acrylic polymer is poor, and gloss is limited. Moreover, contact of the two resins is limited so strong catalysts must be used, and package stability has been a problem. Also, and particularly with the high molecular weight epoxy resins, organic solvents have been needed for the epoxy emulsions.
To avoid some of these difficulties, water dispersible aliphatic epoxy resins have been used, but these have not been satisfactory because they are less reactive, they do not possess the superior physical properties of the aromatic polyepoxides, and package stabilith has been a problem since strong catalysts are again needed for the epoxy-carboxy cure.
U.S. Pat. No. 4,028,294 discloses a two phase latex having an epoxy resin component, which is preferably a water insoluble aromatic polyepoxide incorporated into at least one of the monoethylenic monomers (normally by dissolving), and a monomer which is reactive with the epoxy group (preferably a carboxyl-functional monomer). The monomers in the presence of the epoxy resin are copolymerized in an aqueous emulsion at a temperature below which the epoxy reactive monomer will react with the epoxy groups of the polyepoxide, and in the presence of a free radical polymerization catalyst, to provide a stable latex.
However, the prior art does not disclose a stable crosslinkable latex having an epoxy modified core-shell polymer in aqueous emulsion form, wherein the core polymer comprises an epoxy resin and an ethylenically unsaturated monomer, and the shell polymers comprises an ethylenically unsaturated monomer, and a hydroxyl of carboxyl functional monomer, both the core and shell being free of monomers containing amino groups.
The present invention is also directed to the use if said core-shell latices as a binder in the formation of nonwoven mats to be utilized in areas where heat resistance is important. These mats are useful in a variety of applications such as a component in roofing, flooring and filtering materials.
Specifically, these mats can be used in the formation of asphalt-like roofing membranes such as those used on flat roofs. Polyester mats about one meter in width can be formed, saturated with binder, and dried and cured to provide dimensional stability and integrity to the mats, thus allowing them to be rolled and transported to a converting operation where one or both sides of the mats are coated with molten asphalt. The binder utilized in these mats plays a number of important roles. If the binder composition does not have adequate heat resistance, the polyester mat will shrink when coated at temperatures of 170.degree. to 250.degree. C. with the asphalt. A heat resistant binder is also needed for roofing applications when molten asphalt is used to form seams and, later, to prevent the roofing from shrinking when exposed to elevated temperatures over extended periods of time. Said shrinking would result in gaps or exposed areas at seams where the roofing sheets are joined as well as at the perimeter of the roof.
Since the binders used in these structures are present in substantial amounts, i.e., on the order of about 25% by weight, the physical properties thereof must be taken into account when formulating for improved heat resistance. Thus, the binder must be stiff enough to withstand the elevated temperatures, but must also be flexible at room temperature so that the mat can be rolled or wound without cracking or creating other weaknesses which could lead to leaks during and after impregnation with asphalt.
Binders for use on nonwoven mats have conventionally been prepared from acrylate or styrene/acrylate copolymers. In order to improve the heat resistance thereof, crosslinking functionalities have been incorporated into these copolymers.
Other techniques for the production of heat resistant roofing materials include those described in U.S. Pat. No. 4,539,254 involving the lamination of a fiberglass scrim to a polyester mat thereby combining the flexibility of the polyester with the heat resistance of the fiberglass.
This invention also relates to the use of these novel core-shell latices as laminating adhesives which form flexible laminates having high bond strength, and a high degree of both humidity and water resistance. These adhesives are prepared and employed in emulsion form, and on removal of the aqueous medium subsequent to application, the adhesives will cure harden at room temperature to form a flexible laminate having high bond strength, heat resistance, and a high degree of both humidity and water resistance.
The core-shell latices of the present invention are also useful in providing laminates of woven and non-woven fabrics where the fabric itself is of cotton, polyolefin, polyester, polyamide (nylon), etc.; coated and uncoated paper and paperboard; film such as polyvinylidene chloride (PVDC), polyester, PVDC coated polyester, oriented and non-oriented polyethylene and polypropylene film, metallic foils and metallized films; and flexible cellular material such as polyurethane foams or sponge rubber. These laminates can be made of similar or dissimilar laminae and are useful in a wide variety of end-use applications including for example flexible packaging, graphic arts and industrial uses such as weather stripping and electrical insulation.
The packaging industry, particularly the food packaging area thereof, is currently utilizing large quantities of flexible films. Since all properties desired in such laminates are not available in any one specific film the industry generally employs laminates prepared from a combination of films. Very often these laminates are formed from a film of polyethylene terephthalate (PET), polyamide or cellophane, either uncoated or coated with PVDC laminated to a heat sealable polyolefin film which has been treated by corona discharge for adhesion promotion.
In the prior art, the most satisfactory laminates indicated by industry acceptance have been formed with organic solvent-based urethane or polyester adhesives. Most of these adhesives ,however, have the disadvantage of requiring organic solvents such as methyl ethyl ketone, ethyl acetate or alcohol in order to form an applicable solution. Due to the desirability of eliminating solvents from such adhesives because of their increasing costs, flammability as well as pollution considerations, the development of an aqueous emulsion adhesive system capable of performing comparably to the solvent adhesives becomes vital to the continued growth of the industry.
Water-borne laminating adhesives have been described in the prior art. For example, U.S. Pat. No. 3,905,931, describes a one-part water-based adhesive composition using an aqueous emulsion of about 55 to 80% of a poly (ethylacrylate), about 4 to 20% of an ethylene-acrylic acid copolymer (about 80 weight percent of ethylene and about 20 weight percent of acrylic acid) and about 8 to 20% of a 1,2-epoxy resin. Upon removal of water, this composition cures to a water-resistant thermally stable adhesive.
Other water-borne, two-part laminating adhesives are known and have been described as based on an aqueous dispersion of:
(a) a copolymer of a vinyl ester and/or an acrylic acid ester and/or further copolymerizable monomer(s), (b) an epoxy resin, and (c) an amine hardener catalyst. PA1 (a) from 1 to 80% by weight core polymer comprising: PA1 (b) from 20 to 99% by weight shell polymer comprising: PA1 (c) an organic compound which is post added to the formed core-shell polymer and has at least one amino functional group, wherein said amino group is available for later reaction with said epoxy resin upon drying to produce a crosslinked polymer product. PA1 (1) dissolving an epoxy resin in at least one ethylenically unsaturated monomer, PA1 (2) emulsification of the epoxy resin (optional depending on the molecular weight of the epoxy resin), PA1 (3) polymerizing said ethylenically unsaturated monomers to form the core, PA1 (4) forming said shell on said core by polymerizing a second monomer composition in the presence of said core, said second monomer composition consisting essentially of 1 to 99.5% by weight of at least one ethylenically unsaturated monomer and 0.5 to 10% by weight of a hydroxyl or carboxyl functional monomer, providing that the monomers in the core and the shell do not contain amino functional groups, and PA1 (5) post-adding an organic compound containing at least one functional amino group to the latex, wherein the amino group is available for later reaction with the epoxy resin upon curing (once the water in the system has evaporated or disappeared) to produce a crosslinked polymeric product. PA1 (a) from 1 to 80% by weight core polymer comprising: PA1 (b) from 20 to 99% by weight shell polymer comprising: PA1 (c) an organic compound which is post-added to the formed core-shell polymer and having at least one amino functional group, wherein said amino group is available for later reaction wit the epoxy upon drying to produce a crosslinked polymer product. PA1 (a) from 1 to 80% by weight core polymer comprising: PA1 (b) from 20 to 99% shell polymer comprising: PA1 (c) an organic compound which is post-added to the formed core-shell polymer and having at least one amino functional group wherein said amino group reacts with said epoxy resin upon drying to produce a crosslinked polymer product. PA1 (a) from 1 to 80% by weight core polymer comprising: PA1 (b) from 20 to 99% by weight shell polymer comprising: PA1 (c) an organic compound which is post-added to the formed core shell polymer and having at least one amino functional group, wherein said amino group reacts with said epoxy resin upon drying to produce a crosslinked polymer product. PA1 (a) from 1 to 80% by weight core polymer comprising: PA1 (b) from 25 to 99% by weight shell polymer comprising: PA1 (c) an organic compound which is post-added to the formed core shell polymer and having at least one amino functional group, wherein said amino group is available for later reaction with the epoxy resin upon drying to produce a crosslinked polymer product.
The adhesives noted above employing an amine hardener catalyst are characterized as two-part adhesives, i.e., they are sold in two parts and must be combined in specified amounts by the user prior to their use in the laminating process. The packaging and selling of these adhesives in two parts (a component comprising an epoxy resin or epoxy resin and vinyl polymer and separate amine catalyst component) is necessary because of the inherent reactivity and instability of the adhesive when the two components are combined. Typically, a completed adhesive where the components have been combined exhibits a pot-life of less than 24 hours.
Because of the many inconveniences and disadvantages associated with the two-component latex compositions, there is considerable industry interest in stable one-part, ready-for-use latex compositions which eliminates formulation and pot-life problems.
Accordingly, there is still a need in industry for water-borne, one-part latex compositions which in use exhibits bond strength, water and humidity resistance, equal to or superior than the current two-part compositions.